Continuous casting can be used in steelmaking to produce semi-finished steel shapes such as ingots, slabs, blooms, billets, etc. During a typical continuous casting process (10), as shown in FIG. 1, liquid steel (2) may be transferred to a ladle (12), where it may flow from the ladle (12) to a holding bath, or tundish (14). The liquid steel (2) may then flow into a mold (18) via a nozzle (20). In some versions, a sliding gate assembly (16) is selectively opened and closed to selectively start and stop the flow of the liquid steel (2) into the mold (18).
A typical continuous casting nozzle (20), or submerged entry nozzle (SEN), is shown in more detail in FIGS. 2 and 3. For instance, the nozzle (20) may comprise a bore (26) extending through the nozzle (20) along a central longitudinal axis (A) to a closed end (28) at a bottom portion (B) of the nozzle (20). As best seen in FIG. 2, the bore (26), at the bottom portion (B), is defined by substantially straight walls of the nozzle (20) that are substantially parallel with the longitudinal axis (A) to form a substantially cylindrical profile. A pair of ports (24) may then be positioned through opposing side surfaces of the nozzle (20) proximally above the closed end (28) of the nozzle (20). Accordingly, the liquid steel (2) may flow through the bore (26) of the nozzle (20), out of the ports (24), and into the mold (18).
As the sliding gate assembly (16) moves to an open position from a closed position to allow the liquid steel (2) to flow into the mold (18), the incoming turbulent steel jet (3) may flow near the wall of the bore (26) of the nozzle (20), as shown in FIG. 4. Such a turbulent steel jet (3) flowing on one side of the bore (26) may produce a swirl as the steel jet (3) reaches the bottom portion (B) of the bore (26) and may be constricted with a well shape at the closed end (28) of the nozzle (20). This swirl may divide the mainstream steel jet (3) into two flow paths (4) in opposite directions when liquid steel (2) is discharged into the mold (18) from the two ports (24). A lubricant, such as a mold powder or mold flux, is generally added to the metal in the mold (18) to prevent the liquid steel (2) from adhering to the surfaces of the mold (18).
In some instances in the prior art, the flow paths (4) of the liquid steel (2) from the ports (24) of the nozzle (20) become uneven and biased such that the liquid steel (2) is directed in a downward direction toward a broad face (19) of the mold (18), as shown in FIGS. 4-8. For instance, in the illustrated embodiment, the ports (24) are aligned to extend outward from the longitudinal axis along a plane (C). As the liquid steel (2) exits the ports (24), the flow path (4) of the liquid steel (2) is offset from the plane (C). Such uneven flow paths (4) of the liquid steel (2) from the nozzle (20) to the mold (18) can form surface defects, such as longitudinal cracks, in the mold (18). This may be due to uneven distribution of mold flux and non-uniform cooling at the meniscus. A poor lubrication may result in temperature gradients provided by direct contact of liquid steel (2) to the surface of the mold (18). These temperature gradients may induce additional thermal stresses to the solidifying steel shell. In peritectic steel grades, this may further produce an increased shrinkage of the steel shell provided by the peritectic phase transformation.
Moreover, such uneven flow paths (4) throughout the mold (18) may produce liquid mold powder entrainment and/or uneven heat transfer. These uneven flow paths (4) may be enhanced when the nozzle (20) starts to clog with clusters of foreign particles in the steel (2). The agglomeration and attachment of these particles at different zones of the body of the nozzle (20) may distort the initial internal geometry, and may thereby change the flow paths (4) in the mold (18). Accordingly, once the nozzle (20) is clogged to a predetermined amount, the nozzle (20) may need to be changed. An increase of nozzle (20) changes during a sequence due to clogging may reduce the quality of the steel (2) as the flow paths (4) in the mold (18) are changed during the time the new nozzle (20) reaches steady state again. Such uneven flow paths (4) may require the mold operator to manually feed mold powder given that the melting rate becomes different and unsteady from one side of the mold (18) to the other.
Accordingly, there is a need to provide a continuous casting nozzle that produces a more uniform flow path of liquid steel into a mold.